Biomedical subjects

C R Barb

Publications and source records attributed to C R Barb.

At least 19 recordsLinked to original sources

PubMed2006

Secreted proteins and genes in fetal and neonatal pig adipose tissue and stromal-vascular cells.

Although microarray and proteomic studies have indicated the expression of unique and unexpected genes and their products in human and rodent adipose tissue, similar studies of meat animal adipose tissue have not been reported. Thus, total RNA was isolated from stromal-vascular (S-V) cell cultures (n = 4; 2 arrays; 2 cultures/array) from 90-d (79% of gestation) fetuses and adipose tissue from 105-d (92% of gestation) fetuses (n = 2) and neonatal (5-d-old) pigs (n = 2). Duplicate adipose tissue microarrays (n = 4) represented RNA samples from a pig and a fetus. Dye-labeled cDNA probes were hybridized to custom microarrays (70-mer oligonucleotides) representing more than 600 pig genes involved in growth and reproduction. Microarray studies showed significant expression of 40 genes encoding for known adipose tissue secreted proteins in fetal S-V cell cultures and adipose tissue. Expression of 10 genes encoding secreted proteins not known to be expressed by adipose tissue was also observed in neonatal adipose tissue and fetal S-V cell cultures. Additionally, the agouti gene was detected by reverse transcription-PCR in pig S-V cultures and adipose tissue. Proteomic analysis of adipose tissue and fetal and young pig S-V cell culture-conditioned media identified multiple secreted proteins including heparin-like epidermal growth factor-like growth factor and several apolipoproteins. Another adipose tissue secreted protein, plasminogen activator inhibitor-1, was identified by ELISA in S-V cell culture media. A group of 20 adipose tissue secreted proteins were detected or identified using the gene microarray and the proteomic and protein assay approaches including apolipoprotein-A1, apolipoprotein-E, relaxin, brain-derived neurotrophic factor, and IGF binding protein-5. These studies demonstrate, for the first time, the expression of several major secreted proteins in pig adipose tissue that may influence local and central metabolism and growth.

Adipose Tissue↗

PubMed2006

Gene expression in the brain-pituitary adipose tissue axis and luteinising hormone secretion during pubertal development in the gilt.

The occurrence of puberty in the female is due to the interplay of central and peripheral mechanisms in which the hypothalamic-pituitary-ovarian axis regulates growth and gonadal function, as well as adipocyte hormone secretion. Hypothalamic GnRH mRNA expression increased at 3.5 months of age and declined by 6 months of age. Concomitant with the age related reduction in the oestrogen negative feedback on LH secretion was a decline in hypothalamic oestrogen receptor-alpha (ERalpha) expression and increased expression of repressor of ER activity gene (REA) at 210 days of age. Hypothalamic proopiomelanocortin expression increased at 6 months of age followed by increased expression of progesterone receptor (PR) membrane compliment-1 and steroid membrane binding protein gene at 210 days of age. This represents development of the endogenous opioid peptide-progesterone dependent LH inhibitory pathway. Adipose tissue leptin and insulin like growth factor-I (IGF-I) gene expression increased with age and adiposity. Pituitary transcription factors, steroidogenic factor 1 (SF1) and Lhx3, and LHbeta and FSHbeta gene expression increased with age. These results identify key hypothalamic and pituitary genes associated with changes in LH secretion and growth during pubertal development and adipose tissue genes and secreted proteins related to maturation of the neuroendocrine axis and puberty.

Adipose Tissue↗

PubMed2005

The control of adenohypophysial hormone secretion by amino acids and peptides in swine.

Several different amino acids and peptides control secretion of adenohypophysial hormones and this control may be indirect, via the modulation of hypothalamic hormone secretion. Indeed, classical hypothalamic hormones (e.g., gonadotropin-releasing hormone [GnRH], growth hormone-releasing hormone [GHRH], somatostatin, etc.) may be released into the hypothalamo-hypophysial portal vasculature, travel to the adenohypophysis and there stimulate or inhibit secretion of hormones. Alternatively, some amino acids and peptides exert direct stimulatory or inhibitory effects on the adenohypophysis, thereby impacting hormone secretion. In swine, the most extensively studied modulators of adenohypophysial hormone secretion are the excitatory amino acids (ExAA), namely glutamate and aspartate, and the endogenous opioid peptides (EOP). In general, excitatory amino acids stimulate release of luteinizing hormone (LH), follicle-stimulating hormone (FSH), growth hormone (GH), and prolactin (PRL). Secretion of adenohypophysial hormones induced by ExAA is primarily, but perhaps not exclusively, a consequence of action at the central nervous system. By acting primarily at the level of the central nervous system, EOP inhibit LH secretion, stimulate GH release and depending on the animal model studied, exert either stimulatory or inhibitory influences on PRL secretion. However, the EOP also inhibited LH release by direct action on the adenohypophysis. More recently, peptides such as neuropeptide-Y (NPY), orexin-B, ghrelin, galanin, and substance P have been evaluated for possible roles in controlling adenohypophysial hormone secretion in swine. For example, NPY, orexin-B, and ghrelin increased basal GH secretion and modulated the GH response to GHRH, at least in part, by direct action on the adenohypophysis. Secretion of LH was stimulated by orexin-B, galanin, and substance P from porcine pituitary cells in vitro. Because the ExAA and various peptides modulate secretion of adenohypophysial hormones, these compounds may play an important role in regulating swine growth and reproduction.

Amino Acids↗

PubMed2005

Leptin: a metabolic signal affecting central regulation of reproduction in the pig.

The discovery of the obesity gene and its product, leptin, it is now possible to examine the relationship between body fat and the neuroendocrine axis. A minimum percentage of body fat may be linked to onset of puberty and weaning-to-estrus interval in the pig. Adipose tissue is no longer considered as only a depot to store excess energy in the form of fat. Recent findings demonstrate that numerous genes, i.e., relaxin, interleukins and other cytokines and biologically active substances such as leptin, insulin-like growth factor-I (IGF-I), IGF-II and Agouti protein are produced by porcine adipose tissue, which could have a profound effect on appetite and the reproductive axis. Hypothalamic neurons are transsynaptically connected to porcine adipose tissue and may regulate adipose tissue function. In the pig nutritional signals such as leptin are detected by the central nervous system (CNS) and translated by the neuroendocrine system into signals, which regulate appetite, hypothalamic gonadotropin-releasing hormone (GnRH) release and subsequent luteinizing hormone (LH) secretion. Furthermore, leptin directly affects LH secretion from the pituitary gland independent of CNS input. Changes in body weight or nutritional status are characterized by altered adipocyte function a reduction in adipose tissue leptin expression, serum leptin concentrations and a concurrent decrease in LH secretion. During pubertal development serum leptin levels, hypothalamic leptin receptor mRNA and estrogen-induced leptin gene expression in fat increased with age and adiposity in the pig and this occurred at the time of expected puberty. In the lactating sow serum and milk leptin concentrations were positively correlated with backfat thickness and level of dietary energy fed during gestation as well as feed consumption. Although, these results identify leptin as a putative signal that links metabolic status and neuroendocrine control of reproduction, other adipocyte protein products may play an important role in regulating the reproductive axis in the pig.

Adipose Tissue↗

PubMed2005

Neuropeptide Y modulates growth hormone but not luteinizing hormone secretion from prepuberal gilt anterior pituitary cells in culture.

Pituitary cells, from seven 160- to 170-day-old pigs, were studied in primary culture to determine the affects NPY on LH and GH secretion at the level of the pituitary. On day 4 of culture, medium was discarded, plates were rinsed twice with serum-free medium and cells were cultured in 1 ml fresh medium without serum and challenged individually with 10(-10), 10(-8) or 10(-6) M [Ala(15)]-h growth hormone-releasing factor-(1-29)NH(2) (GRF); 10(-9), 10(-8) or 10(-7) M GnRH or 10(-9), 10(-8), 10(-7) or 10(-6) M NPY individually or in combinations with 10(-9) or 10(-8) M GnRH or 10(-8) or 10(-6)M GRF. Cells were exposed to treatment for 4 h at which time medium was harvested and quantified for LH and GH. Basal LH secretion (control; n = 7 pituitaries) was 12 +/- 6 ng/well. Relative to control at 4 h, 10(-9), 10(-8) and 10(-7) M GnRH increased (P < 0.01) LH secretion by 169, 176 and 197%, respectively. Neuropeptide-Y did not alter (P > 0.4) basal LH secretion nor 10(-8) M GnRH-induced increase in LH secretion but 10(-9) M GnRH-stimulated LH secretion was reduced by NPY and was not different from control or GnRH alone. Basal GH secretion (control; n = 7 pituitaries) was 56 +/- 12 ng/well. Relative to control at 4 h, 10(-10), 10(-8) and 10(-6) M GRF increased GH secretion by 111%, 125% (P < 0.01) and 150% (P < 0.01), respectively. Only 10(-6) M (134%) and 10(-7) M (125%) NPY increased (P < 0.04) basal GH secretion. Addition of 10(-9), 10(-8) and 10(-7) M NPY in combination with 10(-8) M GRF suppressed (P < 0.04) GRF-stimulated GH secretion. However, 10(-9) M NPY enhanced (P < 0.06) the GH response to 10(-6) M GRF. These results demonstrate that NPY may directly modulate GH secretion at the level of the pituitary gland.

Analysis of Variance↗

PubMed2004

Orexin-B modulates luteinizing hormone and growth hormone secretion from porcine pituitary cells in culture.

To test the hypothesis that orexin-B acts directly on the anterior pituitary to regulate LH and growth hormone (GH) secretion, anterior pituitary cells from prepuberal gilts were studied in primary culture. On day 4 of culture, 10(5) cells/well were challenged with 0.1, 10 or 1000 nM GnRH; 10, 100 or 1000 nM [Ala15]-hGRF-(1-29)NH2 or 0.1, 1, 10 or 100 nM, orexin-B individually or in combinations with 0.1 and 1000 nM GnRH or 10 and 1000 nM GRF. Secreted LH and GH were measured at 4 h after treatment. Basal LH and GH secretion (control; n = 6 pigs) was 183 +/- 18 and 108 +/- 4.8 ng/well, respectively. Relative to control at 4 h, all doses of GnRH and GRF increased (P < 0.0001) LH and GH secretion, respectively. All doses of orexin-B increased (P < 0.01) LH secretion, except for the 0.1 nM dose. Basal GH secretion was unaffected by orexin-B. Addition of 1, 10 or 100 nM orexin-B in combinations with 0.1 nM GnRH increased (P < 0.001) LH secretion compared to GnRH alone. Only 0.1 nM (P = 0.06) and 100 nM (P < 0.001) orexin-B in combinations with 1000 nM GnRH increased LH secretion compared to GnRH alone. All doses of orexin-B in combination with 1000 nM GRF suppressed (P < 0.0001) GH secretion compare to GRF alone, while only 0.1 nM orexin-B in combination with 10 nM GRF suppressed (P < 0.01) GH secretion compared to GRF. These results indicate that orexin may directly modulate LH and GH secretion at the level of the pituitary gland.

Animals↗

PubMed2004

Role of leptin in the regulation of gonadotropin secretion in farm animals.

The recently discovered protein, leptin, which is secreted by fat cells, has been implicated in regulation of feed intake or energy balance and the neuroendocrine axis in rodents, humans and large domestic animals. Leptin was first identified as the gene product found to be deficient in the obese (ob/ob) mouse. Administration of leptin to ob/ob mice restored reproduction as well as reducing feed intake and causing weight loss. The leptin receptor (LR) which has been cloned and is a member of the class 1 cytokine family of receptors, is found in the brain and pituitary of all species studied to date. Neuropeptide Y has been proposed as the primary mediator of leptin action in the hypothalamus to regulate luteinizing hormone (LH) and growth hormone (GH) secretion. In vitro studies using both hypothalamic explants and pituitary cell culture provided evidence that supports a direct action of leptin at the level of brain and pituitary gland in the pig, but only the pituitary in cattle. Central administration of leptin increased LH secretion in the fasted cow and ewe, but not in control fed animals, indicating that metabolic state is an important factor in modulating the hypothalamic-pituitary response to leptin. Changing serum leptin concentrations and leptin mRNA expression were associated with onset of puberty in heifers and gilts. Thus, leptin appears to be an important link between metabolic status and the neuroendocrine axis.

Animals↗

PubMed2004

Role of leptin in modulating the hypothalamic-pituitary axis and luteinizing hormone secretion in the prepuberal gilt.

Three experiments (EXP) were conducted to test the hypothesis that leptin modulates LH, GnRH, and neuropeptide Y (NPY) secretion. In EXP I, prepuberal gilts received intracerebroventricular (i.c.v.) leptin injections and blood samples were collected. In EXP II, anterior pituitary cells from prepuberal gilts in primary culture were challenged with 10(-14), 10(-13), 10(-12), 10(-11), 10(-10), 10(-9), 10(-8), 10(-7), or 10(-6) M leptin individually or in combinations with 10(-10), 10(-9), and 10(-8) M GnRH. In EXP III, hypothalamic-preoptic area (HYP-POA) explants were placed in perfusion system and exposed to 0 (n=5), 10(-12) M (n=4), 10(-10) M (n=4), 10(-8) M (n=4), or 10(-6) M (n=5) human recombinant leptin (LEP) for 30 min. In EXP I, serum LH concentrations were unaffected by leptin treatment. In EXP II, all doses of leptin increased LH secretion except for 10(-12) and 10(-7) M. Only 10(-7), or 10(-13) M leptin in combination with 10(-8) or 10(-9) M GnRH, respectively, suppressed LH secretion. In EXP III, prior to leptin, media GnRH concentrations were similar across treatments. Media GnRH concentrations increased after 10(-12), 10(-10), and 10(-8) M leptin compared to control. Leptin treatment failed to influence NPY secretion across treatments. These results indicate that components of the neuroendocrine axis that regulate GnRH and LH secretion are functional and leptin sensitive before the onset of puberty. Other neural peptides in addition to NPY may mediate the acute effects of leptin on the GnRH-LH system and lastly, the inability of i.c.v. leptin treatment to increase LH secretion may in part be related to stage of sexual maturation and associated change in negative feedback action of estradiol on LH secretion.

Animals↗

PubMed2004

The role of melanocortin-3 and -4 receptor in regulating appetite, energy homeostasis and neuroendocrine function in the pig.

A recently discovered class of receptors, melanocortin-3 and -4 receptor (MC3/4-R), are located within the brain and modulate feed intake in rodents. Stimulation of the receptor (agonist) inhibits feed intake whereas blockade (antagonist) of the receptor increases intake. Our knowledge of factors regulating voluntary feed intake in humans and domestic animals is very limited. i.c.v. administration of an MC3/4-R agonist, NDP-MSH, suppressed (P<0.05) feed intake compared with controls at 12, 24, 48 and 72 h after treatment in growing pigs. Fed pigs were more responsive to the MC3/4-R agonist then fasted animals. However, i.c.v. treatment with MC3/4-R antagonist, SHU9119, failed to stimulate intake. The failure of MC3/4-R antagonist to stimulate feed intake suggests involvement of other brain hormone(s) which antagonize the action of SHU9119 at the MC3/4-R, blocking its stimulatory effect on intake. Treatment with NDP-MSH or SHU9119, across a wide dose range, failed to affect LH and GH secretion, except for the 10 micro g dose of NDP-MSH, which exhibited both a stimulatory and an inhibitory effect on GH secretion in fasted animals. Treatment with agouti-related peptide, a natural brain hormone that blocks the MC3/4R, failed to stimulate feed intake. These results do not support the idea that endogenous melanocortin pays a critical role in regulating feed intake and pituitary hormone secretion in the pig. SHU9119 blocked the NDP-MSH-induced increase in cAMP in HEK293 cells expressing the porcine MC4-R sequence without the missense mutation. The EC(50) and IC(50) values were similar to the human MC4-R, confirming that SHU9119 is a pig MC4-R antagonist. However, pigs were heterozygous for an MC4-R gene missense mutation. It is possible that the MC4-R mutation alters function and this may explain the failure to demonstrate MC3/4-R involvement in modulating feeding behavior and LH and GH secretion in the pig.

Animals↗

PubMed2003

Are hypothalamic neurons transsynaptically connected to porcine adipose tissue?

Specific anatomical sites and pathways responsible for mediating metabolic and neuroendocrine effects of leptin are still poorly understood. Therefore, we examined distribution of leptin receptor-containing neurons transsynaptically connected with the porcine fat tissue by means of combined viral transneuronal tracing and immunohistochemical staining method. Pseudorabies virus (PRV) was injected into the perirenal fat tissue in pigs, and after survival periods of 3, 5, 7, 9, and 11 days, hypothalami were processed immunohistochemically with primary antisera against PRV and leptin receptor (OBR). PRV labeled neurons were found in paraventricular nucleus (PVN), ventromedial nucleus (VMN), anterior hypothalamic area (AHA), preoptic area (PA), arcuate nucleus (ARC), and supraoptic nucleus (SON) by nine days after injection of the virus. Double-labeling immunofluorescence demonstrated that OBR were co-localized in nearly all virus-infected neurons. The present results provide the first morphological data demonstrating a multisynaptic circuit of neurons of CNS origin which innervates porcine fat tissue.

Adipose Tissue↗

PubMed2003

Growth hormone releasing factor decreases long form leptin receptor expression in porcine anterior pituitary cells.

Pituitary cells from six pigs, 180-200 days of age, were studied in primary culture to determine if growth hormone releasing factor (GRF) affects long form leptin receptor (Ob-Rl) expression. On Day 4 of culture, 10(5) live cells per well were challenged with either 0, 10(-6), 10(-7) or 10(-8)M [Ala15]-hGRF-(1-29)NH(2) (3 wells per treatment per pig). Secretion of growth hormone (GH) into the media and pituitary Ob-Rl mRNA expression were determined at 4 h after treatment. Media were analyzed for GH by radioimmunoassay, and total RNA was isolated from cells for determination of Ob-Rl expression by semi quantitative reverse transcription PCR. Basal GH concentration was 32+/-2 ng per 10(5) cells per well (n=18 wells) for 4 h. Relative to control at 4 h, 10(-6),10(-7) and 10(-8)M GRF increased (P<0.01) GH secretion by 151, 129 and 120%, but decreased (P<0.05) Ob-Rl expression by 32, 50 and 38%, respectively. These results indicate that GRF directly modulates Ob-Rl expression at the level of the pituitary, and thereby playing a role in regulating pituitary sensitivity to leptin.

Animals↗

PubMed2002

Distribution of neurons containing leptin receptors in the hypothalamus of the pig.

Leptin, secreted by white adipocytes, has profound feeding, metabolic, and neuroendocrine effects. Leptin acts on the brain, but specific anatomical sites and pathways responsible for mediating these effects are still unclear. We have systematically examined the distribution of leptin receptor containing neurons in the porcine hypothalamus by means of immunohistochemical staining methods. Leptin receptor immunoreactivity (OBR-IR) was observed in both the preoptic area and anterior hypothalamic area. No immunoreactive structures were found in the median eminence. Only single, small neurons were observed in the arcuate nucleus. The most abundant OBR-IR cell bodies were located in the supraoptic nucleus. In the paraventricular nucleus, OBR-IR neurons were moderate in number. Single, dispersed neurons were found in the ventromedial nucleus. These findings indicate that there are distinct OBR-IR neuronal populations in the porcine hypothalamus and leptin not only plays an integrative role in feeding behavior, but also in neuroendocrine activity.

Animals↗

PubMed2002

Leptin receptors, NPY, and tyrosine hydroxylase in autonomic neurons supplying fat depots in a pig.

The goal of this study was to determine the immunohistochemical characteristics of peripheral adrenergic OBR-immunoreactive (OBR-IR) neurons innervating adipose tissue in a pig. The retrograde tracer, Fast Blue (FB), was injected into either the subcutaneous, perirenal, or mesentery fat tissue depots of three male and three female pigs each with approximately 50 kg body weight. Sections containing FB(+) neurons were stained for OBR, tyrosine hydroxylase (TH) or neuropeptide Y (NPY) using a double labeling immunofluorescence method. OBR, TH, and NPY immunoreactivities were present in the thoracic (T) and lumbar (L) ganglia of the sympathetic chain, as well as in the coeliac superior mesenteric ganglion (CSMG), inferior mesenteric ganglion (IMG), intermesenteric ganglia (adrenal-ADG, aorticorenal-ARG, and ovarian-OG or testicular-TG ganglion). These results indicate that, in addition to neuroendocrine functions, leptin may affect peripheral tissues by acting on receptors located in sympathetic ganglion neurons.

Adipose Tissue↗

PubMed2002

Effects of N-methyl-D,L-aspartate on LH, GH, and testosterone secretion in goat bucks maintained under long or short photoperiods.

Photoperiod modulates reproduction in goats. We tested the hypothesis that the excitatory glutamatergic tone is reduced in the photoinhibited goat. The objectives of this study were to determine the effect of photoperiod and glutamatergic stimulation on LH, GH, and testosterone (T) secretion in goat bucks. Eight mature, intact bucks were used in two simultaneous 4 x 4 Latin square designs. Variables were two photoperiod regimens (short day; SD, 10 h light:14 h dark, n = 4; vs long day; LD, 16 h light:8 h dark, n = 4) and four doses of N-methyl-D-L-aspartate (NMA; 0, 1, 2 and 4 mg/kg BW, i.v.). Venous blood was obtained for 2 h before and after NMA injection, followed by GnRH injection and then a final 1 h of sampling. Injection of NMA increased (P < 0.002) LH secretion within 20 min. This increase was sustained for 120 min, but the response was most pronounced in LD goats. The increase in mean LH was associated with a concomitant dose-dependent increase in pulse frequency (P < 0.006). However, NMA treatment had no effect (P > 0.10) on LH pulse amplitude. The release of LH after injection of GnRH was not affected by photoperiod. Exposure of bucks to LD reduced T secretion relative to that of SD bucks (P < 0.01). However, GH secretion was enhanced in LD bucks (P< 0.001). The response of GH to NMA was dependent on photoperiod history. A highly significant immediate and sustained increase (P < 0.001) was observed in LD but not in SD bucks within 10 min. Overall, a dose-dependent increase (P < 0.01) in T secretion was stimulated by NMA in both LD and SD bucks. These results indicate that NMA receptors may be involved in the regulation of LH, GH, and testosterone secretion in the goat. Furthermore, length of day influences GH secretion in the goat and NMA receptor activation had divergent effects on the secretion of this hormone.

Animals↗

PubMed2002

Metabolic regulation of the neuroendocrine axis in pigs.

Transition from the fed to fasted state occurs more rapidly in prepubertal pigs than in mature pigs. Insulin-like growth factor I (IGF-I), leptin and specific metabolites, such as glucose and free fatty acids (FFA), play a role in signalling metabolic status to the brain-pituitary axis. High serum concentrations of FFA or glucose suppressed the growth hormone (GH) response to GH releasing hormone (GHRH), whereas glucose inhibited and FFA enhanced pituitary LH response to GnRH. The site of action of FFA and glucose on LH and GH secretion is at the pituitary cell. In cultured pig pituitary cells, IGF-I suppressed the GH response to GHRH and enhanced basal LH secretion. However, intracerebroventricular injection of IGF-I failed to affect LH or GH secretion in prepubertal gilts. Acute fasting suppressed leptin secretion without affecting LH or GH secretion. Metabolic fuel restriction by decreasing glucose availability increased GH secretion, but decreased LH secretion in prepubertal gilts. However, serum leptin concentrations were unchanged. Thus, the effects of acute energy deprivation on LH and GH secretion are independent of changes in leptin secretion. Serum leptin concentrations, hypothalamic leptin receptor mRNA and oestrogen-induced leptin gene expression in fat increased with age and adiposity in pigs. This increase occurred at the time of expected puberty in intact pigs. An intracerebroventricular injection of leptin suppressed feed intake, but stimulated GH secretion in prepubertal gilts. Leptin stimulated GnRH release from hypothalamic tissue in vitro. These results identify putative signals that link metabolic status and neuroendocrine control of appetite, growth and reproduction and have implications for nutrition-related human health problems due to high fat diets.

Animals↗

PubMed2001

Serum leptin concentrations, luteinizing hormone and growth hormone secretion during feed and metabolic fuel restriction in the prepuberal gilt.

Two experiments were conducted to determine 1) the effect of acute feed deprivation on leptin secretion and 2) if the effect of metabolic fuel restriction on LH and GH secretion is associated with changes in serum leptin concentrations. Experiment (EXP) I, seven crossbred prepuberal gilts, 66 +/- 1 kg body weight (BW) and 130 d of age were used. All pigs were fed ad libitum. On the day of the EXP, feed was removed from four of the pigs at 0800 (time = 0) and pigs remained without feed for 28 hr. Blood samples were collected every 10 min from zero to 4 hr = Period (P) 1, 12 to 16 hr = P 2, and 24 to 28 hr = P 3 after feed removal. At hr 28 fasted animals were presented with feed and blood samples collected for an additional 2 hr = P 4. EXP II, gilts, averaging 140 d of age (n = 15) and which had been ovariectomized, were individually penned in an environmentally controlled building and exposed to a constant ambient temperature of 22 C and 12:12 hr light: dark photoperiod. Pigs were fed daily at 0700 hr. Gilts were randomly assigned to the following treatments: saline (S, n = 7), 100 (n = 4), or 300 (n = 4) mg/kg BW of 2-deoxy-D-glucose (2DG), a competitive inhibitor of glycolysis, in saline iv. Blood samples were collected every 15 min for 2 hr before and 5 hr after treatment. Blood samples from EXP I and II were assayed for LH, GH and leptin by RIA. Selected samples were quantified for glucose, insulin and free fatty acids (FFA). In EXP I, fasting reduced (P < 0.04) leptin pulse frequency by P 3. Plasma glucose concentrations were reduced (P < 0.02) throughout the fast compared to fed animals, where as serum insulin concentrations did not decrease (P < 0.02) until P 3. Serum FFA concentrations increased (P < 0.02) by P 2 and remained elevated. Subcutaneous back fat thickness was similar among pigs. Serum IGF-I concentration decreased (P < 0.01) by P 2 in fasted animals compared to fed animals and remained lower through periods 3 and 4. Serum LH and GH concentrations were not effected by fast. Realimentation resulted in a marked increase in serum glucose (P < 0.02), insulin (P < 0.02), serum GH (P < 0.01) concentrations and leptin pulse frequency (P < 0.01). EXP II treatment did not alter serum insulin levels but increased (P < 0.01) plasma glucose concentrations in the 300 mg 2DG group. Serum leptin concentrations were 4.0 +/- 0.1, 2.8 +/- 0.2, and 4.9 +/- 0.2 ng/ml for S, 100 and 300 mg 2DG pigs respectively, prior to treatment and remained unchanged following treatment. Serum IGF-I concentrations were not effected by treatment. The 300 mg dose of 2DG increased (P < 0.0001) mean GH concentrations (2.0 +/- 0.2 ng/ml) compared to S (0.8 +/- 0.2 ng/ml) and 100 mg 2DG (0.7 +/- 0.2 ng/ml). Frequency and amplitude of GH pulses were unaffected. However, number of LH pulses/5 hr were decreased (P < 0.01) by the 300 mg dose of 2DG (1.8 +/- 0.5) compared to S (4.0 +/- 0.4) and the 100 mg dose of 2DG (4.5 +/- 0.5). Mean serum LH concentrations and amplitude of LH pulses were unaffected. These results suggest that acute effects of energy deprivation on LH and GH secretion are independent of changes in serum leptin concentrations.

Animals↗

PubMed2001

Biology of leptin in the pig.

The recently discovered protein, leptin, which is secreted by fat cells in response to changes in body weight or energy, has been implicated in regulation of feed intake, energy expenditure and the neuroendocrine axis in rodents and humans. Leptin was first identified as the gene product found deficient in the obese ob/ob mouse. Administration of leptin to ob/ob mice led to improved reproduction as well as reduced feed intake and weight loss. The porcine leptin receptor has been cloned and is a member of the class 1 cytokine family of receptors. Leptin has been implicated in the regulation of immune function and the anorexia associated with disease. The leptin receptor is localized in the brain and pituitary of the pig. The leptin response to acute inflammation is uncoupled from anorexia and is differentially regulated among swine genotypes. In vitro studies demonstrated that the leptin gene is expressed by porcine preadipocytes and leptin gene expression is highly dependent on dexamethasone induced preadipocyte differentiation. Hormonally driven preadipocyte recruitment and subsequent fat cell size may regulate leptin gene expression in the pig. Expression of CCAAT-enhancer binding proteinalpha (C/EBPalpha) mediates insulin dependent preadipocyte leptin gene expression during lipid accretion. In contrast, insulin independent leptin gene expression may be maintained by C/EBPalpha auto-activation and phosphorylation/dephosphorylation. Adipogenic hormones may increase adipose tissue leptin gene expression in the fetus indirectly by inducing preadipocyte recruitment and subsequent differentiation. Central administration of leptin to pigs suppressed feed intake and stimulated growth hormone (GH) secretion. Serum leptin concentrations increased with age and estradiol-induced leptin mRNA expression in fat was age and weight dependent in prepuberal gilts. This occurred at the time of expected puberty in intact contemporaries and was associated with greater LH secretion. Further work demonstrated that leptin acts directly on pituitary cells to enhance LH and GH secretion, and brain tissue to stimulate gonadotropin releasing hormone secretion. Thus, development of nutritional schemes and (or) gene therapy to manipulate leptin secretion will lead to practical methods of controlling appetite, growth and reproduction in farm animals, thereby increasing efficiency of lean meat production.

Adipose Tissue↗

PubMed2001

Opioid and cholecystokinin antagonists alleviate gastric inhibition of food intake by premeal loads of casein in meal-fed rats.

This study was undertaken to determine whether casein, compared with its constituent amino acids, given at the onset of a meal, would influence intake due to cholecystokinin (CCK) or opioid activity. Male Sprague-Dawley rats (n = 80; 225 g) were given either premeal loads of casein or its constituent amino acids and treated with opioid or CCK antagonists in a 2 x 4 factorially designed experiment. During a 21-d period, rats were meal-fed by restricting access to food to 5 h/d. The rats were fed the AIN-93 diet with soy isolate substituted for casein as the dietary protein source. On d 7-21, rats were given oral premeal loads of 5 mL of a 50 g/L casein or constituent amino acid solution before meal-feeding. On d 14-21, 20 rats were injected intraperitoneally with one of the following treatments: saline, naltrexone (l mg/kg), naloxone methiodide (5 mg/kg) or lorglumide (1 mg/kg) before the premeal load and feeding. Antagonist treatments increased intake (P < 0.05) by 15.3% compared with saline treatment (7.82 vs. 9.02 g/d) in rats given premeal loads of casein. Intake of rats given premeal loads of amino acids was not influenced by antagonists. At 2 h after feeding on d 21, the rats were killed, bled and eviscerated. Effects of antagonists on stomach and intestinal mass, digesta contents and fecal output were also dependent on the type of premeal load, indicating that gastric retention of digesta due to casein was mediated by CCK and opioids. Body weight accretion, liver, and epididymal fat mass and blood concentrations of specific amino acids changed in the same manner as intake (P < 0.05). Serum insulin was greater (P < 0.05) in casein-treated rats and reduced (P < 0.01) by opioid antagonists. Satiety associated with premeal loads of casein is related to changes in gastrointestinal function of meal-fed animals and involves both opioid and CCK regulation.

Amino Acids↗